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Sputhe Positrac arrived today [pics]

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  #31  
Old 04-23-2009, 11:46 AM
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I just got off the phone with Jeff at Sputhe Engineering. The new front bracket with an offset mounts so that the offset is away from the frame. Thus the correct orientation is to the left. He also said the way to mount this is one bolt at a time to prevent the engine dropping like it did when I tried to install the TT. The True-Track folks really do need to pull those "instructions" that were done by some magazine that say to remove all the isolator bolts at the same time. That is a recipe for disaster, even if you've got the engine supported by a jack.



Will be installing this later today (hopefully).
 
  #32  
Old 04-23-2009, 12:48 PM
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Originally Posted by Gary7
...The use of either a front or rear stabilizer makes lateral flex of the motor mount a non-issue because it allows for absolutely fixed lateral positioning of the drivetrain and swingarm assembly. With either a front or rear stabilizer installed, the drivetrain and swingarm can no longer move laterally no matter what the condition of the motor mounts...
It takes 3 points to define a plane. If you have links on 2 points and a flexible link on the 3rd, you have not defined a plane. You still have a mount that allows flex in an undesireable dimension. Your rear mount without the stabilizer will still be allowed to flex just as much as it did before. You will feel less sway or wallow though as you'll be restricting the front motor mount's flex.

Think of it like this. The stock setup with 1 link atop the engine acts as a pivot point for the engine. Any side load against the rear wheel (as in leaning over in a corner) will result in the swingarm acting as a lever forcing the engine to pivot about the top motor mount. The amount of this pivot is only limited by the condition of the 2 motor mounts.

If you were to hold the frame ridigdy and push the rear wheel right, the swingarm would end up pivoting the engine about the top link; the rear of the engine would move right, and the front of the engine would move left.

If you place a link on just the front motor mount to resist this left or right movement at the front of the motor, the rear of the motor is still allowed to move. The rear motor mount is still allowed to flex as much as it did before. The drivetrain and swingarm can still move laterally no matter what the condition of the motor mounts. This absolutely does not fix lateral positioning of the drivetrain and swingarm assembly.

You will definitely feel a tightening up of the bike. And as you've said, it will probably be just fine for your riding style.

Keep us posted.
 
  #33  
Old 04-25-2009, 09:27 AM
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If you want to follow this topic as far as a ride report, click here.
 
  #34  
Old 04-25-2009, 10:05 AM
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Originally Posted by mtnlvr
It takes 3 points to define a plane. If you have links on 2 points and a flexible link on the 3rd, you have not defined a plane.
True. But assuming you're dealing with a rigid object (the engine/tranny/swingarm assembly) and a single pivot point (the top stabilizer), preventing lateral movement on either side of the pivot point will prevent it on the other side of the pivot point as well:

 
  #35  
Old 04-25-2009, 11:17 AM
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Originally Posted by Gary7
...preventing lateral movement on either side of the pivot point will prevent it on the other side of the pivot point as well...
Sorry man, but that is not how it works out. The only way that would work is if the top link were actually an axle running down through the center of the motor. Then limiting the lateral movement on either side of the axle would limit movement on the other side (like a fat kid one one side of a teeter totter and a skinny kid on the other). But this is not the case here, all you've done is changed the engine's pivot from a point to a line.

With the original top link only, the engine was free to rotate in any direction about a point, the top link, only limited by the flex of the motor mounts.

With the addition of another link, the engine movement is more defined as it can only revolve about a line, an imaginary axis drawn between the two links, as well as rock within the frame, now limited by the flex of the motor mount without the link. The flex of the remaining naked motor mount allows the rear wheel to move laterally (albeit in more of a controlled circular path about the axis defined by these two links).

Adding the third link limits engine movement to a single plane defined by the three links. The only movement allowed is a rocking motion about that plane.
 
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  #36  
Old 04-25-2009, 12:35 PM
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Originally Posted by SC-Longhair
Thanks Newhawk.

Now if I could just buy everything I need (want) right now, I'd be a happy guy. Wouldn't we all?

Ricors, new front springs, TT or PT, new rear springs. An easy $1,000 and then some.
You and me both. If I had my druthers I'd be putting the Ricors up front, Works in the back, and the TT or PT...then I'd be a happy man.
 
  #37  
Old 04-25-2009, 09:45 PM
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Originally Posted by mtnlvr
Sorry man, but that is not how it works out. The only way that would work is if the top link were actually an axle running down through the center of the motor. Then limiting the lateral movement on either side of the axle would limit movement on the other side (like a fat kid one one side of a teeter totter and a skinny kid on the other). But this is not the case here, all you've done is changed the engine's pivot from a point to a line.

With the original top link only, the engine was free to rotate in any direction about a point, the top link, only limited by the flex of the motor mounts.

With the addition of another link, the engine movement is more defined as it can only revolve about a line, an imaginary axis drawn between the two links, as well as rock within the frame, now limited by the flex of the motor mount without the link. The flex of the remaining naked motor mount allows the rear wheel to move laterally (albeit in more of a controlled circular path about the axis defined by these two links).

Adding the third link limits engine movement to a single plane defined by the three links. The only movement allowed is a rocking motion about that plane.
Personal experience is that adding the 3rd (rear link) finishes what feels right to me.
 
  #38  
Old 04-25-2009, 10:24 PM
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More elegant, a bent metal bracket? HAHAHAHAHAHA
 
  #39  
Old 04-25-2009, 10:31 PM
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Originally Posted by rayfinseats
More elegant, a bent metal bracket? HAHAHAHAHAHA
 
  #40  
Old 04-26-2009, 01:08 PM
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Originally Posted by mtnlvr
The flex of the remaining naked motor mount allows the rear wheel to move laterally (albeit in more of a controlled circular path about the axis defined by these two links).
I follow you now:



Would you not agree that the amount of deflection is greatly reduced with the addition of the front stabilizer because now for the drivetrain to pivot around an axis defined by the top and front stabilizer the rear mount not only must deflect on the horizontal, it also has to compress on the vertical? The construction and design of the isolator itself is designed to prevent just this sort of deformation.
 


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